The invention is related to the field of electrostatography and more specifically to liquid developing systems employed therein.
The formation and development of images on an imaging surface which may be the surface of a photoconductor, by electrostatic means is well known. The basic xerographic process, as disclosed by C. F. Carlson in U.S. Pat. No. 2,297,691 involves placing a uniform electrostatic charge on a photoconductive insulating layer exposing the layer to a light-and-shadow image to dissipate and charge on the areas of the layer exposed to the light, and developing the resulting charge pattern by depositing on the image a finely-divided marking material referred to in the art as "toner". The toner will normally be attracted to those areas of the layer which retain a charge, thereby forming a toner image corresponding to the charge image. This powder image may then be transferred to a support surface such as paper. The transferred image may subsequently be permanently affixed to a support surface as by heat. Instead of latent image formation by uniformly charging a photoconductive layer and then exposing the layer to a light-and-shadow image, one may form the charge pattern by directly charging an imaging surface in image configuration. The powder image may be fixed to the imaging surface if elimination of the powder image transfer step is desired. Other suitable means such as solvent or overcoating treatment may be substituted for the foregoing heat fixing steps.
Several methods are known for applying a developer to a charge pattern to be developed. One development method as disclosed by E. N. Wise in U.S. Pat. No. 2,618,552 is known as "cascade" development. Another method of developing charge patterns is the "magnetic brush" process as disclosed for example, in U.S. Pat. No. 2,874,063. Still another development technique is the "powder cloud" process as disclosed by C. F. Carlson in U.S. Pat. No. 2,221,776.
An additional dry development system involves developing a charge pattern with a powdered developer material, the powder having been uniformly applied to the surface of a powder applicator. The charge pattern is brought close enough to the developer powder applicator so that the developer powder is pulled from the powder applicator to the charge bearing image in image configuration. The charge pattern and powder applicator may desirably be brought in contact including contact under pressure to effect development. The powder applicator may be either smooth surfaced or roughened so that the developer powder is carried in the depressed portions of the patterned surface. Exemplary of this system are the techniques disclosed by H. G. Greig in U.S. Pat. No. 2,811,465.
Liquid development may also be employed in the development of charge patterns. In conventional liquid development, more commonly referred to as electrophoretic development, an insulating liquid vehicle having finely divided solid material dispersed therein contacts the imaging surface in both charged and uncharged areas. Under the influence of the electric field associated with the charged image pattern the suspended particles migrate toward the charged portions of the imaging surface separating out of the insulating liquid. This electrophoretic migration of charged particles results in the deposition of the charged particles on the imaging surface in image configuration.
An additional liquid technique for developing charge patterns is the liquid development process disclosed by R. W. Gundlach in U.S. Pat. No. 3,084,043. In this method, a charge pattern is developed or made visible by presenting to the imaging surface a liquid developer on the surface of a developer dispensing member having a plurality of raised portions defining a substantially regular patterned surface and a plurality of portions depressed below the raised portions. The depressed portions contain a liquid developer which is maintained out of contact with the imaging surface. When the raised areas of the developer applicator are brought into contact with the imaging surface bearing a charge pattern the developer creeps up the sides of raised portions in contact only with the charged area of the imaging surface, and is deposited thereon.
This technique is to be distinguished from conventional liquid development wherein there is an electrophoretic movement of charged particles suspended in a liquid carrier vehicle to the charged portion of the image bearing surface while the liquid substantially remains on the applicator surface and serves only as a carrier medium. In the liquid development method described by R. W. Gundlach in U.S. Pat. No. 3,084,043 the liquid phase actively takes part in the development of the image since the entire liquid developer is attracted to the charged portions of the image bearing surface. Furthermore, in the liquid development method described by R. W. Gundlach unlike conventional liquid development, the developer liquid contacts only the charged portions of the image bearing surface.
A further liquid development technique is that referred to as "wetting development" or selective wetting as described in U.S. Pat. No. 3,285,741. In this technique an aqueous developer uniformly and continously contacts the entire imaging surface and due to the selected wetting and electrical properties of the developer substantially only the charged areas of the normally hydrophobic imaging surface are wetted by the developer. The developer should be relatively conductive having a resistivity generally from about 10.sup.5 to 10.sup.10 ohm cm and have wetting properties such that the wetting angle measured when the developer is placed on the imaging surface is smaller than 90.degree. at the charged areas and greater than 90.degree. in the uncharged areas.
In a compact electrostatographic copying device employing the development techniques disclosed by R. W. Gundlach, the imaging surface and the liquid developer applicator are desirably small diameter cylinders or the like, to facilitate the cooperative movement of the surfaces in contact during development in a confined space. Such moving contact between the imaging surface and the applicator resulting in the transfer of liquid developer from the applicator to the photoreceptor occurs at development speeds ranging generally from about 2 to about 70 inches per second.
Prior imaging surfaces and the applicators have generally been rigid and have been manufactured by machining large castings to the proper diameter within precise tolerances. A functional surface such as a photoconductive film or a patterned applicator surface may subsequently be applied to the casting to achieve the necessary high degree of precision desirable for the proper functioning of the surface in an electrostatographic apparatus. Although, these prior imaging and applicator surfaces reproduce a large volume of high quality images before replacement is required, an appreciable savings of time, money and effort may be realized by employing a special expandable support cylinder as an integral part of the machine to allow the replacement of a substantially less expensive relatively thin outer sleeve.
It has been proposed in copending application of Stephen C. P. Hwa, entitled Roller Arrangement, filed in the name of Xerox Corporation Sept. 7, 1973 (UK application No. 42182/73) that one of the cooperating surfaces (either the photoreceptor or the applicator) be deformable, having a hardness of from about 30.degree. to 90.degree. (shore A durometer) while retaining the functional integrity of its operative surface. The use of a deformable surface when at least one of such surfaces is arcuate, provides substantially uniform contact and a substantially uniform nip width between the surfaces.
Such an arrangement in effect compensates for a range of dimensional irregularities in the non-deformable surface so that substantially uniform density, good image quality and high resolution are achieved in the final copy. Resilient imaging and applicator surfaces are desirable to obtain good density and resolution, particularly in connection with the development method disclosed by R. W. Gundlach in U.S. Pat. No. 3,084,043.
A method of making a resilient surface, especially one for use in accordance with the techniques of S. C. P. Hwa as described above is sought. Such a surface which is capable of being assembled easily, without special tools and at the site of use is desirable.
It is, therefore, an object of this invention to provide a development system devoid of the above noted deficiencies.
A further object of this invention to provide an improved resilient arcuate surface.
Another object of this invention is to provide a novel development system.
Those and other objects of this invention are accomplished generally speaking by for example providing a resilient arcuate member which comprises a rigid support member and a flexible arcuate surface spaced apart by a resilient member and a means for tensioning the resilient member in such a way that the spacing dimension is reduced an amount sufficient to allow easy movement of the flexible surface with respect to the resilient member.
In another embodiment of the instant invention there is provided a method for assembling a resilient arcuate member which comprises providing a rigid support, a flexible arcuate surface, a resilient member and an extending means for the resilient member; tensioning the extending means so that the resilient member is reduced in one dimension an amount sufficient to allow placement of the resilient member between the rigid support and the flexible surface; placing the resilient member between the rigid support and the flexible surface; and relaxing the tension on the extending means so that the flexible sleeve is placed apart from the support means.
When the resilient member is in a relaxed position, it is under sufficient compression between the flexible surface and the support means to prevent the surface from moving easily with respect to the support and to impart a functional firmness to the flexible surface. The resilient member may be tensioned so that its spacing dimension is reduced. Such a reduction relaxes the compression between the flexible surface and the support means sufficient to allow easy movement of the flexible surface with respect to the support means.